Enable*
之前的文章用到了一些Enable*开头的注解，比如EnableAsync、EnableScheduling、EnableAspectJAutoProxy、EnableCaching等，Enable表示开启/允许一项功能。
Enable*工作原理
我们只需要几个很简单的注解就能开启一个复杂的功能，这是多么简易的用法，这是怎么办到的？
首先来看看计划任务@EnableScheduling的源代码
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Import(SchedulingConfiguration.class) @Documented public @interface EnableScheduling { }
主要核心的配置就是导入了一个配置文件，所以谜底也就接开了。
@Import(SchedulingConfiguration.class)
来看看Import的源码
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface Import { /** * {@link Configuration}, {@link ImportSelector}, {@link ImportBeanDefinitionRegistrar} * or regular component classes to import. */ Class<?>[] value(); }
1、Configuration
即上面的用法，直接导入Configuration配置类。
根据条件选择导入不同的配置类，参考@EnableAsync
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Import(AsyncConfigurationSelector.class) public @interface EnableAsync {
public class AsyncConfigurationSelector extends AdviceModeImportSelector<EnableAsync> { private static final String ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME = "org.springframework.scheduling.aspectj.AspectJAsyncConfiguration"; /** * {@inheritDoc} * @return {@link ProxyAsyncConfiguration} or {@code AspectJAsyncConfiguration} for * {@code PROXY} and {@code ASPECTJ} values of {@link EnableAsync#mode()}, respectively */ @Override public String[] selectImports(AdviceMode adviceMode) { switch (adviceMode) { case PROXY: return new String[] { ProxyAsyncConfiguration.class.getName() }; case ASPECTJ: return new String[] { ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME }; default: return null; } } }
3、ImportBeanDefinitionRegistrar
动态注册Bean，参考@EnableAspectJAutoProxy
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Import(AspectJAutoProxyRegistrar.class) public @interface EnableAspectJAutoProxy {
class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar { /** * Register, escalate, and configure the AspectJ auto proxy creator based on the value * of the @{@link EnableAspectJAutoProxy#proxyTargetClass()} attribute on the importing * {@code @Configuration} class. */ @Override public void registerBeanDefinitions( AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry); AnnotationAttributes enableAspectJAutoProxy = AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class); if (enableAspectJAutoProxy.getBoolean("proxyTargetClass")) { AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry); } if (enableAspectJAutoProxy.getBoolean("exposeProxy")) { AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry); } } }
